The present invention relates to a pressure-actuated snap switch with a casing, wherein a connecting link is supported by spring tension in a bearing. The switching operation is under control of a bolt guided in the switch casing. The bolt itself is controlled by a ram passing through the casing wall and bearing upon the longer lever arm of a lever pivotably mounted in the casing.
In order to initiate a switching action in such a snap switch, it is necessary for a force acting upon the operating ram, to be sufficiently high to force a snap spring over the dead-center position and, optionally, to tension an additional restoring spring. The force which has to be applied is several times greater than that producing the contact pressure. Thus, if a minimum contact pressure is required, this presupposes the action of a correspondingly higher force on the operating ram. In applications where only limited forces are available for operating the switch, as for example when the switch is to be tripped by shock waves in the medium surrounding it, the attainable contact pressure is normally limited.
It has been known to use a compression spring to actuate the ram by pretensioning the spring to such an extent that the force or tension stored therein is lower than that necessary for initiating the switching operation. Thus, in this embodiment only a small additional force acting on the operating ram is necessary for initiating the switching operation. In order to be able to better adapt such a snap switch to the operating conditions, it has also been proposed in connection with this embodiment to operate the operating ram via a lever and not directly. An auxilliary ram acts upon the lever, and a pretensioned opposing spring adjustable counter to the operation of the auxiliary ram acts on the lever. This embodiment suffers from the disadvantage that there are two springs, which partly reciprocally compensate one another and consequently make the construction more complicated and expensive. Moreover, during operation, the length of the opposing spring and consequently the force stored therein is significantly changed.